1. Field Of The Invention
The present invention relates to a method of manufacturing integrated circuits and other electronic devices. More particularly, the invention relates to an improved process for the forming and etching of tungsten containing film on a semiconductor wafer.
2. Description Of The Related Art
Refractory metals such as chemical vapor deposited tungsten have been identified as suitable interconnect material for VLSI/ULSI applications. As interconnect dimensions shrink to the micron and submicron range, sputtered materials become unsuitable for the needs of high density, high speed devices. Chemical vapor deposited tungsten is finding applications in the area of gate and interconnect technology due to its electromigration resistance, excellent step coverage, and because its thermal expansion is similar to that of silicon. Chemical vapor deposited tungsten also withstands higher process temperatures and does not form hillock as will aluminum.
In the past hard masks and hard stopping layers have been used to manufacture semiconductor devices with chemical vapor deposited tungsten interconnects. A manufacturable etch process, however, must use photoresist as the mask and be able to stop on oxide while allowing long overetches to occur. The etchant must be selective to both photoresists and oxide and have good critical dimension control. Additionally, the typical chemical vapor deposited tungsten film is topologically very rough, usually 25% or more of the film thickness and therefore puts more emphasis on a selective etchant than in the case of a smoother sputtered film.
Chemical vapor deposited tungsten forms a volatile fluoride product, as does silicon dioxide. Thus, it becomes very difficult to achieve selectivity between the two films. Chlorine-based chemistries and oxychlorides have been successful in etching tungsten with selectivity to oxide. These chemistries, however, tend to erode an organic mask, e.g. a photoresist, at the same rate as that of the tungsten which makes it difficult to the process the thick chemical vapor deposited tungsten with submicron geometries. The height-to-minimum geometry aspect ratio of the starting photoresist layer would most likely have to exceed 2:1. The use of one micron or smaller chemical vapor deposited tungsten for metal interconnects has made it necessary to develop a two step process that encompasses all of the necessary selectivities and critical dimension control and a process which makes tungstens interconnects truly manufacturable. It is also necessary to achieve sufficient selectivity between chemical vapor deposited tungsten and oxide.